Your, your spouse and your children all have your own -- very packed -- schedules. Juggling the multiple schedules doesn't have to be a nightmare. You can get this all under control.
The first thing you'll need is a calendar so everyone's information is all in one place. You can use a paper calendar to hang in the kitchen or try an online calendar (there are plenty of free ones to try). Once you have a calendar, add everything to it: holidays, games, appointments, birthdays, etc. As soon as something new comes up, add it immediately to the calendar. You want to add five basic pieces of information for each event: who, what where, when and how.
Once you have your calendar, check it daily and use it to plan ahead. Let it be your guide when scheduling new appointments, so no one day gets too hectic (or any more hectic than it need be). You can also use your calendar to get a sense of people's workloads and where you can find some efficiency. Do you notice that the same spouse is doing all the driving for the children? What other arrangements can be made to help lighten that spouse's load?
A key to really managing schedules well is to prioritize. Look at each individual's schedule on the calendar --- is there no free time? Keeping the family's schedule manageable is a great opportunity to teach your kids about prioritizing and making choices among activities. Should they prioritize based on the other people involved in the activity, costs associated with the activity, or what they really enjoy and want to commit to?
Of course, one of the most important reasons to manage the family's schedule isn't just so everything gets done, but so you can be sure you've got family time scheduled. When you spot open time on everyone's schedule, block if off as family time -- quickly.